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Abstract

An output block for an in-system programmable analog integrated circuit. The output block features an output amplifier that accepts a differential current-mode input signal and provides a single-ended output voltage. The output amplifier is also selectably operable as a linear amplifier, an integrator or a comparator. The output block also includes a common-mode feedback circuit (CMFB), an analog trim circuit (OATRM), a CLAMP circuit, and an offset calibration circuit (CLDAC), all coupled to the differential input of the output amplifier. The CMFB exhibits bandwidth comparable to that of the output amplifier and a drive capability that enables the differential-input to single-ended output conversion. The CLAMP is connected to the differential input in the comparator mode in order to avoid slow recovery from an overdrive condition. The OATRM forces a difference current into the differential input that compensates for a (gain independent) offset voltage that results from various mismatches. The CLDAC uses a digital-to-analog converter (DAC) to perform offset calibration at the differential input of the output amplifier. In addition, the output block is configured to be operational in a number of user-selectable modes, including, in one embodiment, one or more of: a linear (NORM) mode, a comparator (COMP) mode, and an integrator (INT) mode. An amplifier in the output block is variously reconfigured to achieve the selected mode of operation. Also, the output block accommodates an autocalibration (CAL) technique by clamping the single-ended output stage and balancing, through operation of the CLDAC, signals at an input node and at an interstage node of the amplifier.

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